A technology disclosed herein relates to volume management of a storage system, and more particularly, to volume management for maintaining performance of the storage system which includes virtualized volumes.
One of storage system virtualization technologies is a virtual logical volume (hereinafter, simply referred to as virtual volume) for dynamically allocating a storage area when an I/O request is generated (for example, see JP 2003-15915 A). In a normal logical volume (hereinafter, referred to as real logical volume or simply real volume), storage areas of capacities defined at the time of creation are all reserved beforehand on physical disks or array groups. On the other hand, in a virtual logical volume, no storage area is reserved while a capacity is only defined at the time of creation, and only a necessary amount of a storage area is allocated for the first time when an I/O request is generated for the virtual logical volume. The storage area that has been allocated (or will be allocated) to the virtual logical volume is reserved in an area exclusively used for the virtual logical volume (hereinafter, this area will be referred to as pool). The pool is defined as a group of a plurality of real logical volumes. Hereinafter, the plurality of real logical volumes constituting the pool will be referred to as pool logical volumes or simply pool volumes. An I/O to the virtual logical volume is converted into an I/O to the pool volume in the storage system to be processed.
In the virtual logical volume, it is not necessary to prepare all storage areas of defined capacities beforehand, and a area of a size actually used when an I/O request is generated is dynamically reserved. Thus, use of the virtual logical volume enables an operation where the minimum necessary number of physical disks is mounted when the storage system is introduced, and a physical disk is added when a capacity runs short according to a subsequent use status. By efficiently increasing disk utilization in this way, introduction and operation costs of the storage system can be reduced.
Further, in order to balance I/O loads on the storage system, a technology of migrating a logical volume has been disclosed (for example, see JP 2001-337790 A). According to this technology, the logical volume is migrated to a proper migration destination based on an I/O load or the like on the logical volume. Through this migration, loads concentrated in a specific part are distributed and, as a result, performance dropped because of the load concentration can be improved.